1. Field of the Invention
The invention relates to a protective element that safely dissipates overvoltages which is comprised of a parallel connection of a varistor and an surge arrester.
2. Description of the Related Art
A protective element to dissipate electrical overvoltages is, for example, known from German patent document DE 43 31 215 A1, which discloses such an element comprising a parallel circuit of an surge arrester, an air-spark gap, and a varistor that are arranged in cup-shaped metallic casing. The varistor is annularly fashioned and is directly attached to the surge arrester. A contact pin that is in contact with the upper electrode of the surge arrester is led through the annularly fashioned varistor. Lower electrodes of the surge arrester and upper electrodes of the varistor are connected to the cup-shaped casing.
Such a protective element made from a parallel-circuited varistor and surge arrester has the advantage that, given steeply climbing overvoltages, the spark delay of the surge arrester is bypassed with the aid of the previously indicated varistor. In this manner, the shielding effect of the protective element during the response time of the surge arrester is improved.
However, what is disadvantageous in the known protective element is that the annular varistor exhibits a high self-capacitance. This determines the damping behavior of the protective element when it is applied to high-frequency circuits. A higher capacity thereby leads to higher damping that in turn reduces the conductor lengths that can be realized with such a protective element.
However, in high-frequency telecommunication systems, such as ADSL, VDSL, and others, there is a need for protective elements to dissipate overvoltages that can bypass the reaction time of the surge arrester and simultaneously exhibit a low dampening; such devices are particularly appropriate for the high-frequency systems.